Sealant and adhesive with damping properties

ABSTRACT

A curable sealant, adhesive and coating composition which provides vibration dampening to a substrate to which it is applied. The composition contains from 5% to 40% by weight of 3, 4-polyisoprene, a curing agent, at least one of a liquid rubber or elastomer and at least one additional additive. The composition is applied to the substrate and heat cured.

BACKGROUND OF THE INVENTION

1. Field of the invention

This invention relates to novel compositions for adhesives sealantsand/or coatings containing 3,4-polyisoprenes. More particularly thisinvention involves curable and non-curable compositions for adhesivessealants and/or coatings containing conventional polymeric componentsand in addition 3,4-polyisoprenes. A preferred field of application forthese compositions is the vehicle industry, especially the automotiveindustry.

2. Discussion of Related Art

In the manufacture and assembly of automobiles, adhesives sealants andcoatings are used for a variety of different purposes. Sealants andadhesives are selected mainly on the base of the following properties:

strength, i.e. shear strength, peel strength

elongation, flexibility

durability

ease of application.

For coatings, especially underbody coatings, abrasion resistance is anadditional criterion. In view of reducing the complexity of carmanufacturing and thus reducing manufacturing costs, there is a need for“multifunctional” products, i.e. sealants, adhesives and/or coatingswhich solve additional problems in addition to their prime function.

Contemporary design of vehicles, machines and appliances involves almostexclusively the use of thin gauge sheet metal. Moving parts and runningengines cause vibration of these thin metal structures, which in turncreate noise. Numerous methods for noise abatement are known, however,most of these methods require additional manufacturing steps and/orcomponents which have only the function of vibration damping. A primeexample of the conventional products for vibration damping are highlyfilled bitumen pads. These pads have to be extruded, die-cut and shapedin separate steps. Prior to application they frequently have to be heatformed to fit them to non flat structures and then glued to the carbody, machine or appliance. Numerous attempts have been made to replacethis costly manual procedure by products which can be easily applied byrobots. Plastisol formulations serving the dual function of underbodycoating (projection against abrasion) and acoustic damping have beendescribed in EP-A-358598, or DE-A-3444863. DE-A-4013318 discloses a twolayer underbody coating which performs the dual functions of protectingagainst abrasion and absorbing noise resulting from impact (stones,gravel, water, etc.). Whereas these products/processes are quite usefulfor combining the functions of underbody coating and noise abatement,there still remains a need to combine the function of an adhesive and/orsealant with noise reduction. This is particularly desirable for thoseparts of a car, machine or appliance that do not require a specificcoating for protection against abrasion such as trunk and hood lids,doors or fire walls of a car.

Adhesives and sealants for these parts are normally applied early on inproduction, in the so-called “body shop”. Hence, they are applied to thebare, uncleaned metal which is frequently covered with an oil for rustprotection. Although plastisols, PVC-plastisols in particular, are usedin the body shop, those disclosed in EP-A-358598 or DE-A-3444863 are notsuitable as adhesives/sealants for bare metal substrates. The plastisolformulations which are especially designed for bare metal applicationhave poor to no vibration damping properties.

Another class of adhesives/sealants suitable for body shop applicationare based on rubbers especially vulcanizing compositions based on1,3-polybutadienes and/or 1,3-polyisoprenes. These preferably containliquid, low molecular weight polydienes, sulfur and optionallyaccelerators for sulfur vulcanization. In addition, these formulationsmay contain solid high molecular weight rubbers, whereby the liquidpolydiene(s) and/or the solid rubber may contain functional groups suchas hydroxyl groups, carboxylic groups, anhydride groups or epoxy groups.This class of rubber based adhesives/sealants has been the subject ofvarious patent applications, e.g. EP-A-97394, EP-A-309903, DE-A-3834818,DE-A-4120502, DE-A-4122849, EP-A-181441 and EP-A-356715. AlthoughDE-A-4122849 and EP-A-181441 mention a potential use of thesecompositions for vibration damping and/or sound damping, no reference ismade to the efficacy of these compositions for vibration damping,because to the best of applicant's knowledge these materials have notbeen used for their combined adhesive/sealant and vibration dampingproperties. The use of 3,4-polyisoprenes for sealants, adhesives andcoatings has thus far not been described.

SUMMARY OF THE INVENTION

In accordance with the present invention, it has been found that3,4-polyisoprene can be combined with other curable or non-curableliquid and/or solid rubbers or liquid polyolefins to provide adhesiveand sealant formulations with superior vibration damping properties.Surprisingly, the incorporation of 3,4-polyisoprenes intosealant/adhesive formulations does not have a detrimental effect onother desired properties of the formulations, i.e. applicability, curingspeed, adhesion, strength and/or elasticity.

DETAILED DESCRIPTION OF THE INVENTION

In addition to 3,4-polyisoprene, sealant/adhesive formulations accordingto the present invention may contain at least one of the followingitems:

one or more liquid or solid rubbers or elastomers

thermoplastic polymers in the form of finely divided powders

fillers

tackifiers and/or adhesion promoters

plasticizers/extenders

curatives, accelerators, catalysts

stabilizers, antioxidants

rheology improvers.

3,4-polyisoprenes according to this invention are polyisoprenes with asignificant content of at least 30%, and preferably 55% to 70% of3,4-polyisoprene, as determined by NMR-spectroscopy. Although thepreferred 3,4-polyisoprenes are high molecular weight (MW) polymers,i.e. MW 200000 and above, it can be advantageous for some formulationsto use low molecular weight liquid 3,4-polyisoprenes as additives toconventional plastisols, for example.

The compositions according to this invention may contain up to 40% byweight of 3,4-polyisoprene, preferably less than 20% by weight of3,4-polyisoprene, and more preferably 5% to 15% by weight of3,4-polyisoprene. Acoustical damping characteristics can be variedaccording to the amount of 3,4-polyisoprene added, as evidenced bycorresponding changes in the loss factor. To a lesser extent, theeffective useful temperature range over which the loss factor isincreased also appears to be somewhat dependent upon the amount of3,4-polyisoprene added.

Suitable additional liquid rubbers or elastomers can be selected fromamong the following homo- and/or copolymers: polybutadienes, especiallythe 1,3- and 1,2-polybutadienes which may have terminal and/or pendantfunctional groups such as hydroxy-, carboxylic acid-, carboxylicanhydride-, or epoxy groups, polybutenes, polyisobutylenes,1,4-polyisoprenes, styrene-butadiene-copolymers, butardieneacrylonitrile copolymers, polyurethanes and polyepoxides. The MW of theliquid rubbers is typically below 20000, preferably between 2000 and10000. The amount of liquid rubbers in the composition depends upon thedesired rheology of the uncured formulation and the desired mechanicalproperties and acoustic damping properties of the cured formulation. Ingeneral, the amount of liquid rubbers or elastomers varies from about 5to 50 percent by weight.

Suitable solid rubbers, which usually have a significantly higher MWthan the liquid rubbers (100000 or higher), include polybutadiene(preferably with high cis-1,4-content), styrene butadiene rubber,butadiene acrylonitrile rubber, isoprene rubber, butyl rubber andpolyurethane rubber.

Examples of thermoplastic polymers are polypropylene, polyethylene,thermoplastic polyurethanes, methacrylate copolymers, styrene copolymersand PVC.

Fillers can be selected from a wide variety of materials includingchalk, calciumcarbonate (natural ground or precipitated), silicates,barytes and carbon black. Also, flake type fillers such as vermiculite,mica, talc or similar layered silicates are suitable. In someformulations such flake type fillers have shown improved vibrationaldamping efficacy. The total amount of fillers can vary between 10 to 70percent by weight, with the preferred range from 25 to 60 percent byweight.

Tackifiers and/or adhesion promoters may include hydrocarbon resins,phenolic resins, terpene phenolic resins, modified or unmodified rosinacids and esters, polyamines, polyaminoamides, polyepoxy resins andanhydrides and anhydride-containing copolymers.

The type and amount of tackifier(s) depends upon the polymer compositionof the sealant/adhesive, the strength of the cured composition, and thesubstrate to which the sealant/ adhesive is applied. Typical tackifierresins such as the terpene phenolic resins or rosin derivatives aregenerally used in concentrations of about 5 to 20 percent by weight, andpreferably between 7 and 15 percent by weight. Typical adhesionpromoters such as polyamines or polyaminoamides are normally used in therange from about 0.5 to about 10 percent by weight.

A great number of products are suitable for use as plasticizers orextenders, including C₄- to C₁₄-dialkylesters of phthalic acid and C₄-to C₁₄-dialkylesters of C₃- to C₈-dicarboxylic acids, as exemplified bydioctyladipate, aliphatic, aromatic or naphthenic oils, low molecularweight polybutenes or polyisobutylenes, high boiling hydrocarbon fluidsand mixtures thereof. The rheology of the uncured formulation and themechanical properties including the vibration damping can be influ-encedto a certain extent by the amount of plasticizer and/or extender.Generally, plasticizer(s)/extender(s) are used in the range of 5 to 40percent by weight.

Appropriate curatives, accelerators or catalysts depend upon thereactive and/or functional groups of the polymers selected. For curingthe olefinic double bonds of liquid or solid rubbers, including3,4-polyisoprene, a sulfur vulcanizing system is used.

A variety of organic and inorganic accelerators can be used alone, or incombination with sulfur powder. Examples of these accelerators aremercaptobenzothiazoles, dithiocarbamates, sulfenamides, disulfides suchas dibenzothiazole disulfide and/or thiuram disulfides, aldehyde amineaccelerators, guanidines and metal oxides such as zinc oxide. Inaddition, other typical rubber vulcanizing agents such as fatty acids(e.g. stearic acid) may be present in the formulation. The amount ofsulfur can vary widely from zero (in unvulcanized systems) to about 15percent by weight, preferably to about 10 percent. Similarly, the amountof accelerator(s) can vary between zero and about 10 percent. The amountof metal oxides is in the range of zero to about 10 percent.

Stabilizers may be used for protection against thermal, thermooxidativeor ozone degradation. They can be selected from among conventionalstabilizers such as sterically hindered phenols or amines. The amount ofstabilizer used is usually in the range of 0.1 to 5 percent by weight.

Although rheology is normally adjusted by the appropriate type andamount of fillers, conventional rheology improvers such as fumed silicasor bentonites can be present in the range of about 0.1 to 7 percent byweight. In addition, other conventional additives may be present in theformulations.

The acoustical damping efficacy of the compositions according to thepresent invention can be tailored to the specific needs of theapplication with respect to the maximum loss factor and the temperaturerange of the effective loss factor. The governing parameters are thevulcanizing system (amount of sulfur, amount of accelerator) and therubbers incorporated. To a lesser extent, the fillers also influence themaximum loss factor and the corresponding temperature. In addition, thethickness of the applied material influences the damping factor, wherebyfoamed materials exhibit a higher damping factor, although this may notbe applicable in cases where a high tensile strength is required for theadhesive. In most cases, it is desirable that the peak value of the lossfactor should occur approximately at room temperature (about 20° C.) andthat a sufficiently high loss factor be achieved over a broadtemperature range. The curing conditions for the adhesive/sealantcompositions according to the invention can be tailored to the specificapplication; usually, the curing takes place at temperatures between 80°C. and 240° C. in 10 to 35 minutes.

The present invention may be further appreciated by reference to thefollowing specific examples. As will be readily apparent to one skilledin the relevant art, these examples are illustrative of variousparameters of the present invention, but they in no way limit its scope,except to the extent that any parameters shown in the examples may beincorporated into the appended claims.

The damping property (dissipation or loss factor) in these examples wasdetermined according to the Oberst method (DIN 53440) on steel stripswhich had been coated with a defined layer of the adhesive/sealantcomposition, followed by curing in a conventional laboratory oven.

All parts given in the formulations below are parts by weight unlessotherwise stated.

EXAMPLES 1-5

The following components were thoroughly mixed in a Z-blade kneader:

1 2 3 4 5 3,4-polyisoprene¹⁾ 10 10 10 10 10 chalk²⁾ 35 31.5 31 31 31precipitated calciumcarbonate³⁾ 24 25 25 25 24 terpene phenolic resin⁴⁾10 10 10 10 10 naphthenic 5 5 5 5 5 polyisobutylene⁶⁾ 15 15 15 15 15antioxidant⁷⁾ 1 1 1 1 1 calciumoxide⁸⁾ 0 1 1 1 1 zinc oxide, active 0 11 1 1 sulfur powder 0 0 0.5 0 1.0 Dibenzothiazole disulfide (MBTS) 0 0.50.5 1.0 1.0 Lap shear strength (MPa)^(a)) 0.06 n.a. n.a. n.a. 1.2 ¹⁾3,4content (according to NMR) approx. 60%, Mooney viscosity 65/100° C.(ML4) ²⁾natural ground, median particle size 4.5 μm ³⁾stearate coated,median particle size 0.07 μm ⁴⁾Dertophene T (RTM), softening point93-97° C. (ball and ring) ⁵⁾Nyflex 820 (RTM), Nynas-Petroleum ⁶⁾OppanolB 10 (RTM), BASF ⁷⁾N,N′-Di(1,4-dimethylpentyl)-1,4-phenylenediamine⁸⁾Coated with stearic acid ⁹⁾2 mm layer between steel cupons, cured 30min at 155° C., cohesive failure.

Comparative Example 1

A PVC plastisol was prepared by mixing the following components:

paste grade emulsion PVC 32.0 dioctylphthalate 30.0 natural ground chalk16.5 precipitated calciumcarbonate 6.0 calciumoxide 3.0 metal oxides(colour pigments) 1.0 carbon black 0.1 stabilizer 1.0 adhesion promoter2.0 fumed silica 0.4 hydrocarbon extender 8.0

EXAMPLE 6 Comparative Example 2 (Comp.2)

The following ingredients were thoroughly mixed in a Z-blade kneader.

Comp. 2 6 7 solid rubber¹⁾ 2.7 — — 3,4-polyisoprene²⁾ — 5.0 10.0 liquidpolybutadiene³⁾ 8.9 8.9 7.0 liquid polybutadiene⁴⁾ 17.8 15.5 12.0carboxylated polybutadiene^(5a)) 8.9 8.9 — benzylatedpolybutadiene^(5b)) — — 8.0 precipitated calciumcarbonate⁶⁾ 12.1 12.112.1 chalk⁷⁾ 12.1 12.1 12.0 talc 18.6 18.6 21.0 calciumoxide 5.6 5.6 5.5carbon black 0.5 0.5 0.1 antioxidant⁸⁾ 0.5 0.5 0.5 zinc oxide, active4.3 4.3 4.0 sulfur powder 3.0 3.0 2.5 Dibenzothiazole disulfide (MBTS)5.0 5.0 5.3 Lap shear strength (MPA)^(a)) 1.4 1.5 1.2/1.8 ¹⁾high cis-1,4(98%) polybutadiene, Mooney viscosity 48/100° C. (ML4) ²⁾3.4 contentapprox. 60% (according to NMR), Mooney viscosity 65/100° C. (ML4), ³⁾MWapprox. 1800, cis 1,4-content: approx. 72% ⁴⁾MW approx. 1800,vinyl-content: approx. 40-50%, ^(5a))polybutadiene/maleic anhydrideadduct, MW approx. 1700, ^(5b))polybutadiene with terminalbenzylgroups., MW approx. 900 ⁶⁾stearate coated, median particle size0.07 μm, ⁷⁾natural, ground, median particle size 4.5 μm⁸⁾N,N′-Di(1,4-dimethylpentyl)1,4-phenylmediamine. ⁹⁾2 mm layer betweensteel, comp. example 2 and example 6, cured 30 min at 155° C.; example 7cured 30 min at 170° and 30 min at 200° C. respectively, cohesivefailure in all cases.

Acoustic Damping Properties

Spring steel strips 240 mm×10 mm, 1 mm thick were coated on a 200 mmlong section with a layer of the compositions described in examples 1 to6 and comparatative examples 1 and 2. The coating thickness is givenbelow. The coated steel strips were cured in a laboratory oven for 30min at 190° C., unless otherwise stated. The cured strips weresubsequently submitted to a bending vibration test according to DIN53440 (Oberst-Method). As can be seen from FIGS. 1 to 3, thecompositions containing 1,4-polyisoprene exhibit a significant dampingfactor at normal service temperatures (−10° C. to 30° C.), moreover,examples 2 to 5 demonstrate clearly, that by slightly changing in thevulcanizing system, one can optimize the temperature range of maximumloss factor to the desired region. Example 6 and 7 demonstrate thatincorporation of 3.4-polyisoprene into conventional vulcanizing rubbersealant/adhesives (comparatative example 2) improves the damping factorof the cured sealant/adhesive significantly without sacrificing on theshear strength property.

Also, example 7 shows clearly that a higher curing temperature increasesthe shear strength of the cured adhesive although one probably mightexpect this. But surprisingly, also the vibration damping as measured bythe Oberst method is increased, in addition this increased dampingfactor is observed over a broader temperature range compared to the sameformulation cured at the lower temperature, see curve 14 vs curve 15 ofFIG. 3.

Explanation of FIGS. 1 to 3

FIGS. 1 to 3 show graphs of the combined loss factor at 200 Hz of thecoated steel strips versus temperature according to DIN 53440 part 3.The test samples were prepared as described above. Most of the sampleshave been prepared at two different coating thicknesses to compensatefor normal thickness deviations between different formulations.

FIG. 1 shows the loss factor of a conventional PVC-plastisol fromcomparative example 1 (1,2) versus a composition according to example 1(3,4).

curve formulation coating thickness 1: comp. example 1, 2.27 mm 2: comp.example 1, 4.52 mm 3: example 1, 2.2 mm 4: example 1, 4.5 mm.

FIG. 2 illustrates how the factor and the temperature range over which asignificant loss factor is observed (loss factor >0.1) can be varied byslight changes in the composition of the vulcanizing agents.

curve formulation coating thickness 5: example 2, 2.0 mm 6: example 2,2.45 mm 7: example 3, 2.6 mm 8: example 3, 3.5 mm 9: example 4, 2.0 mm10: example 4, 2.65 mm 11: example 5, 4.8 mm.

FIG. 3 shows that the loss factor of a conventional vulcanized rubbercomposition of comparative example 2 is insignificant at normal servicetemperatures of a car (−5° C. to 30° C.) whereas the compositions of theinventive examples 6 and 7 have a significant loss factor at the normalservice temperatures:

curve formulation coating thickness 12: example 2 3.0 mm 13: example 63.1 mm 14: example 7 2.3 mm 15: example 7 2.3 mm 16: example 7 4.4 mm.

All sealant/adhesive formulations of examples 1 to 7 had in addition totheir superior damping properties the necessary properties for use assealant/adhesive for body shop applications in the automotive industry.

What is claimed is:
 1. A curable composition which when cured providesvibration dampening properties to thin gauge steel sheets and which isuseful as a sealant, adhesive or coating consisting essentially of (a)from 5 to 40% by weight of 3,4-polyisoprene, (b) at least one curingagent, (c) at least one liquid rubber or elastomer, and (d) at least oneadditional member selected from the group consisting at finely dividedpolymer powders, fillers, adhesion promoters, plasticizers and liquidextenders, wherein said composition is curd after application to saidthin gauge steel sheets.
 2. A composition as claimed in claim 1 whereinsaid rubber is selected from the group consisting of homo- andcopolymers of polybutadienes, 1,4-polyisoprenes, polyisobutylenes,polybutenes, styrene-butadiene-rubber, polyurethanes and polyexpoxides.3. A composition as claimed in claim 1 wherein said curing agent isselected from the group consisting of vulcanizing agents consisting ofsulfur, an organic accelerator, dicyanodiamide, carboxylic acidanhydrides and polyurethane catalysts.
 4. A composition as claimed inclaim 1 wherein said plasticizer or liquid extender is selected from thegroup consisting of C₄- to C₁₄-dialkylesters of phthalic acid, C₄- toC₁₄-dialkylesters of C₃- to C₈-dicarboxylic acid, aliphatic oils,aromatic oils, naphthenic oils, low molecular weight polybutenes, lowmolecular weight polyisobutylenes, high boiling hydrocarbon fluids, andmixtures thereof.
 5. A composition as claimed in claim 1 wherein saidadhesion promoter is selected from the group consisting of hydrocarbonresins, modified rosin acid, unmodified rosin acid, modified rosinesters, unmodified rosin esters, phenolic resins, terpene phenolicresins, epoxy resins, polyaminoamides, polyaminoethers, polymericanhydrides of carboxylic acids, and monomeric anhydrides of carboxylicacids.
 6. A method for joining or sealing joints between thin gaugesteel sheets and providing vibration dampening properties to said steelsheets comprising coating at least one surface of said steel sheets withthe composition of claim 1, assembling said steel sheets, and heatingthe assembled steel sheets to cure said composition.
 7. A method ofcoating thin gauge steel sheets comprising applying the composition ofclaim 1 onto a surface of said steel sheets and heating the coated steelsheets to cure the coating.
 8. A method as claimed in claim 7 whereinsaid applying is by spraying.
 9. A method as claimed in claim 7 whereinsaid applying is by extruding.
 10. A method for sealing, joining, orcoating joints or surfaces of thin gauge steal sheets and providingvibration dampening properties to said steel sheets comprising applyinga composition as claimed in claim 1 to said steel sheets and heating thecomposition to cure said composition.
 11. A method as claimed in claim10 wherein said composition is in the form of a ribbon.
 12. A method asclaimed in claim 10 wherein said composition is in the form of a tape.13. A curable composition which when cured provides vibration dampeningproperties to thin gauge steel sheets and which is useful as a sealant,adhesive or coating which comprises: (a) from 5% to 40% by weight of3,4-polyisoprene; (b) 5% to 50% by weight of at least one liquid rubber;(c) at least one curing agent, and (d) at least one additional memberselected from the group consisting of finely divided thermoplasticpolymer powders, fillers, adhesion promoters, plasticizers, stabilizers,antioxidants and liquid extenders, wherein the composition is curedafter application to the thin gauge steel sheets.
 14. The composition ofclaim 13 further comprising from 10% to 70% by weight of fillers. 15.The composition of claim 13 which comprises: (a) from 5% to 40% byweight of 3,4-polyisoprene; (b) 5% to 50% by weight of liquid rubber;(c) up to about 35% by weight of curing agents, accelerators andcatalysts; (d) 0.1% to 5% by weight of stabilizers, 10% to 70% by weightof fillers, 5% to 20% by weight of tacifiers, 5% to 40% by weight ofplasticizers and extenders, and optionally 0.5% to 10% by weight ofadhesion promoters.
 16. The composition of claim 13 containing from 5%to 20% by weight of 3,4-polyisprene.
 17. The composition of claim 15containing from 5% to 20% by weight of 3,4-polyisoprene.
 18. Thecomposition of claim 1 containing from 5% to 20% by weight of3,4-polyisoprene.